The present invention relates to Servo valve systems which comprise one of the significant logistics components of a gun system for safe and efficient transfer of ammunition. Specifically, the present invention relates to servo valve systems which cooperate, in a majority voting sequence, to enhance gun system ammunition transfer and efficiency by improving reliability, maintainability and performance.
The reliability of an ammunition transfer system is dependent on the efficiency and performance of the valves and controls involved in operating the transfer mechanism. Specifically, servo valves form a critical link in an ammunition transfer system and a malfunction of these components is detrimental to the smooth operation of the transfer mechanism. More specifically, if a pilot valve sticks at any position, the main stage spool of the valve could stroke unpredictably to either endpoint. Valve sticking may occur due to silting, contaminant build-up in the valve seat and similar environmental problems. A malfunctioning pilot valve may result in the actuator accelerating out of control thereby making the ammunition delivery unreliable and susceptible to failure.
Generally, a servo system is a closed loop control system that produces an error signal used to cancel any differences between an output and input command. The error signal drives an actuator that corrects the difference so the output will agree continuously with the input. Prior art three-stage electro-hydraulic servo valves typically use a single pilot valve for main stage spool control. Thus, if the single pilot valve malfunctions, the servo system becomes inoperative because the actuator will not be functional. Failures of this sort are detrimental to guns such as MK 45 gun systems whose readiness and rate of fire depend, to a large part, on the ammunition loading and transfer mechanism.
In a servo system the output variable is measured, fed back and compared to the desired input function at the summing point. The difference between the two values is an indication of the error which must be corrected. This setup generally requires a closed loop system. Closed loop servo systems are classified according to the variable being controlled. The most common forms of control are velocity, position, torque and combinations of these. The present invention relates to a servo valve system which is based on position control. Preferably, a resolver is used in the feedback loop to obtain position control. For example, sensors are used to determine that the shaft of the actuator has arrived at the desired angular position by counting pulses and comparing them with the input and stopping the shaft when the counts are equal. Further, a velocity feedback sensor loop may remain in the system to help in stabilizing it.
A stable servo system will always return to a stable operating state unless there is a component failure. However, the reliability of a weapon handling system could be significantly improved by structuring the servo valve systems in a manner to provide high level of availability and reliability at all times. Current systems do not use a compound set of servo systems which are able to compensate or step-in to perform the designated operation without interruption when a servo system fails. Specifically, as it relates to ammunition handling systems, the inventors are not aware of any system which utilizes a redundant set of servo valve systems which enable automatic switching of operations from a non-functional valve to a functional one based on a comparative error signal.
Accordingly, there is a need to enhance the reliability and availability of the servo valve systems operating in weapon handling equipment. Specifically, the electro-hydraulic valves in use in the MK 45 gun including ammunition handling systems in many other weapon systems, require a reliable servo valve system tailored to provide high reliability within permissible weight and space-volume parameters.
U.S Pat. No. 5,440,966 issued on Aug. 15, 1995, discloses a material hand-off device and process which uses a high performance hydraulic actuator to transfer ammunition. The power levels and speeds at which the actuator operates result in a system that is very sensitive to component failure. Thus, in an attempt to remedy the situation, various concepts were considered. For the most part, the present invention is an innovative solution to the problem encountered in controlling the actuator which operates the ammunition delivery system.
It is one of the objects of the present invention to provide a valve system for ammunition handling systems which is reliable and enables redundancy in case of failure of one or more of the valves. Specifically, the invention provides a microprocessor controlled servo valve system including a plurality of servo valves and transformers having input and output communications with a main stage spool, hereinafter referred to as the main spool, operating an actuator. More specifically, the system of the present invention includes a resolver, device for converting resolver signals to digital signals, a plurality of digital to analog converters, a plurality of error summing devices, a plurality of amplifiers and a plurality of voltage converters. The main stage spool further includes operable connections to the actuator on one side and to the servo valves and linear variable differential transformers (LVDTs) on another side. Furthermore, the actuator is connected to the resolver and the device for converting the resolver signals is connected to the microprocessor on an output side and the resolver on the input side. The microprocessor also includes connections with the digital to analog converters. The error summing devices provide connections to the digital to analog converters on a first side, the plurality of voltage converters on a second side and the plurality of amplifiers on a third side. The amplifiers are also structured to provide input to the servo valves.
It is yet another object of the invention to provide a servo valve system for precisely operating a material handling system to enable exchange and transfer of ammunition between a plurality of cooperative mechanisms. Specifically, the servo valve system includes a control system, an actuator and a main spool. The control system further includes a central microprocessor unit with operable electronic and data connections to a resolver, a digital converter of signals from the resolver, a plurality of digital to analog converters, a plurality of summer devices, a plurality of voltage converters, a plurality of amplifiers, a plurality of servo valve pilots and a plurality of LVDTs. The actuator is preferably connected to the main stage spool at the input side and the resolver at the output side. Further, the main stage spool is connected to the LVDTs and the servo valves.
It is a further object of the invention to provide a servo valve system to drive and control the motions of an ammunition handling system for engagement with a moving target attached to a gun tube rotatable through an arc above and below a horizontal azimuth. The servo system and the ammunition handling system, in combination, preferably include a control system and a main stage spool operable via a set of three electro-hydraulic pilot servo valves. Each of the pilot servo valves, hereinafter referred to as servo valves, are connected to LVDTs and form a configuration in which the set of preferably three servo valves operate the actuator. Further, the ammunition handling system includes a cradle that is matingly engageable with a slide mechanism to transfer the ammunition thereto. Upon transfer to the slide mechanism, the ammunition is ultimately fed into the gun tube. The ammunition handling system therefore includes two dynamic systems. The first system being an actuator driven cradle and the second being a slide that is attached to the gun tube. Both the cradle and the slide are adjustable to raisable and tiltable positions relative to a horizontal azimuth. The actuator includes an extendable dynamic arm that is implemented to raise and lower the cradle for engagement with the slide.
It is yet another object of the present invention to provide a device-implemented method of maintaining the reliability of an ammunition supply system using a plurality of pilot servo valves to supply undiminished power to an actuator for driving an ammunition handling device in which ammunition is transferred to and from a gun chamber. In the preferred embodiment, the method includes the steps of providing at least three servo valves to operate a main stage spool. Further, the method includes operating an actuator while monitoring positions of the main stage spool. The method also includes correcting errors by summing signals from a plurality of digital to analog converters and a plurality of transformer position to voltage converters.
Generally, the majority voting three-stage servo valve system of the present invention incorporates three servo valves for the control of the main stage spool. Each of the servo valves is controlled by a separate electrical main stage spool position feedback control system. The main stage spool position is monitored by a triple redundant set of LVDTs. The result is three servo valves operating independently. This structure provides a feedback control system which is highly reliable and provides an efficient redundancy at a substantially reduced probability of failure.
The above features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.